Mechanochemical changes on cyclometalated Ir(_III) acyclic carbene complexes - design and tuning of luminescent mechanochromic transition metal complexes

A new class of luminescent mechanochromic cyclometalated Ir(_III) complexes with pyridyl acyclic carbene ligands have been developed. These complexes shown predominant MLCT phosphorescence mixed with ³LC character. In the solid state and neat film, the emission of these complexes show significant red-shift upon mechanical grinding. On the basis of XRD, X-ray crystallography, Raman spectroscopy and DFT calculation, the mechanically-induced variations of the molecular packing and the structural conformation have been elucidated. With the understanding of their mechanochemical changes, it enables the design of luminescent mechanochromic compounds with tailored mechanochromic properties, including the emission color and the mechanochromic shift, through judicious structural modifications of the ligands as illustrated in the complexes reported in this work. It would also open up new design of mechanoresponsive materials.